Hi Tenor,
As Buddy stated, the "open circuit" rating is simply what the panels can put out with no load connected.
If you're going to use them with a 24 volt house system, you'll need to connect two panels in series and find a 24 volt controller.
One thing on the broken glass- the glass that they put over solar cells is a special glass that is optimized by reduction of iron content in the glass formula, and it is also antireflective coated, so that it transmits the wavelengths of light that solar cells like, a lot better than regular glass. If you put regular glass or plexiglass over your cells, you will find that the array will put out a lot less than rated power. To do it right you'd have to use the specialty glass.
If you don't really care, it's not a big deal, but using plex or regular glass over the cells can easily turn a 50 watt panel into a 35 watt panel !